1. Field of the Invention
The present invention relates to a spark ignition engine with a fuel injector for injecting fuel directly into the cylinder.
2. Description of the Related Art
Japanese Patent Application No. 4-41102 filed by the same applicant discloses an engine which comprises a hollow combustion chamber formed on an upper surface of the piston, a plug pocket for the ignition plug extending outwardly from the side wall of the combustion chamber, a L-shape step portion formed along a part of the circumference of the combustion chamber, the side wall of which contacts or crosses with the side wall of the plug pocket and a part of which is used as a first fuel guide passage, and a second fuel guide passage formed on the upper portion of the side wall of the combustion chamber so as to contact with the bottom wall of the step portion and leading to the plug pocket. In the above engine, fuel injected in the area from the second fuel guide passage to the bottom wall of the step portion at a low engine load, is directed to the plug pocket along the fuel guide passages while being evaporating by the heat of the piston. At this time, the evaporated fuel is prevented from flowing out the upper surface of the piston by the side wall of the step portion and is surely led into the plug pocket without passing the outside thereof. Thus, the above engine is intended to realize a good stratified charge combustion at a low engine load, by collecting all of injected fuel into the plug pocket as evaporated fuel.
In the above engine, all of injected fuel cannot evaporate until it reaches the plug pocket so that a part amount of injected fuel flows thereinto as liquid fuel. If the engine speed is so low that the time from fuel injection to ignition is relative long, all of the liquid fuel in the plug pocket can evaporate therein during this time and the above good stratified charge combustion can be realized. However, when the engine speed is high, the ignition plug can be inserted into the plug pocket before all of the liquid fuel evaporates. In this case, the liquid fuel can stick onto 10 the ignition portion of the plug so that misfires occur.